<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		ul {
			width: 800px;
			height: 400px;
			border: 1px solid #ccc;
			padding: 0;
			margin: 100px auto;
			list-style: none;
			
			/*指定为伸缩盒子*/
			display: flex;

			justify-content: center;
		}

		li {
			width: 200px;
			height: 200px;
			text-align: center;
			line-height: 200px;
			font-size: 30px;
			background-color: pink;
		}
	</style>
</head>
<body>
	<ul>
		<li>1</li>
		<li>2</li>
		<li>3</li>
	</ul>
</body>
</html>